The objective of this three year project is to define effects of anesthetic drugs on sensory evoked potentials so that effects of anesthetics of these potentials can be separated from effects of surgical manipulation. Evoked potential monitoring will then be more effective in helping to minimize neurologic damage during high risk neurosurgical, vascular and orthopedic operations. During Year 1 we found that diazipam 0.1 mg/kg, droperidol 0.1 mg/kg, feftanyl 0.003 mg/kg and meperidine 1.0 mg/kg alter but do not abolish intermediate latency somatosensory cortical evoked potentials. During Year 2 we will examine the effects of ketamine 2 mg/kg on intermediate latency somatosensory cortical evoked potentials, effects of atropine 0.01 mg/kg on intermediate latency somatosensory and visual evoked potentials, effects of morphine 0.1 mg/kg on somatosensory and visual evoked potentials and effects of halothane (0.15%, 0.5% and 1.5% end tidal concentration) on somatosensory, auditory and visual evoked potentials. In addition we will summarize currently available information on anesthetic management of patients who require intraoperative evoked potential monitoring.